November 25, 2011

If you’re a scientist, then one of the things you need to do is prepare high-quality images for your papers. And, especially if you’re a palaeontologist, or in some other science that involves specimens, that’s often going to mean manipulating photographs. So image editing has become one of those “grey skills”, like word processing and phylogenetic analysis, that you need to have a little of, even if you’re not specialising in that direction.

Here at SV-POW!, none of us is anything remotely approaching wizardly when it comes to image-editing. But we’ve done enough of it that we have a few tips to pass on, so this is the first in an occasional series that will offer some random but relevant hints. (Matt and I both use GIMP, a free image-editing program, but I’m sure PhotoShop has the all the same facilities and more.)

Today: thirty-second colour-balancing. It’s a technique that comes in handy every now and then, especially if you take a lot of specimen photographs in poorly lit basements that make everything look greenish. It came up because in the previous post Matt included this photo of a partially dissected turkey neck:

All the orange made my eyeballs hurt.

So you can spend hours on colour-balancing a photo carefully, and that can be appropriate if you’re preparing a figure for publication. But to fix a photo like this one in thirty seconds, here’s what I do.

Load the image.

Bring up the Layers window and use it to duplicate the layer:

With the top layer selected, choose Colours -> Auto -> Equalize. (There is also a Colours -> Auto -> White Balance option, but I never find that it gives good results.)

Equalize will make the top layer look truly horrible:

Now go back to the Layers window, and play with the top layer’s opacity, so that you get a blend of the original and equalised images:

In this case, I found that 50% opacity looked about the best:

(While it’s still no oil-painting, it’s much better than the all-orange-all-the-time original.)

With the top layer still selected, choose Layers -> Merge Down to make the layers into one, and save the result.

It really does take about thirty seconds total, including the time to start up and shut down the image editor. (Yes, GIMP starts up more quickly than PhotoShop!)

Update (11 April 2012)

If you’re wondering why this is “part 0”, it’s because it was originally posted as a stand-alone article, and we only realised much later that it fits into the tutorial sequence — in particular, the planned multi-part tutorial on preparing illustrations.

Another thing that works quite well, this one at the in-camera stage (assuming your camera can do it) is adjusting the white balance.

Some digital cameras have a bunch of pre-set white balance settings, but also allow for custom white balance. Go into that mode and take a picture, under the same weird lighting conditions that you’re going to be photographing the specimens under, of something you know is white, like a piece of blank paper.

This tells the camera that “THIS IS WHITE” and it will adjust all the colours accordingly.

Grant, in theory you are right, but the white balance is only fool-proof if you really have a truly white sheet of paper handy. One that is at least 120g/cm2, as my camera taught me. 80g/cm2 may no do, because it is too transparent.

Or you could download the free program Irfanview, click Image>Auto Adjust Colours, then click Colour Corrections and reduce saturation (to about -60 or so). For Web photos it’s quicker and easier that firing up the Gimp, Photoshop or Paint Shop Pro.